This invention relates to compositions and processes for the sustained release of drugs. Sustained release compositions or devices for the delayed release of drugs have been used for many years. Such compositions or devices increase the effectiveness of many drugs. Various compositions have been developed, each with a varying degree of success.
For example, the use of drug-containing pellets known as non-pareil seeds has been known since at least 1862. See e.g., U.S. Pat. No. 36,816. Non-pareil seeds are pellets made from sugar and starch. Subsequently, these drug containing pellets came to be coated with a digestible or dispersable delayed release coating. Often, various coatings having different release characteristics would be used on groups of pellets which then would be combined in a single gelatin capsule. As recognized in U.S. Pat. No. 3,119,742, incorporated herein by reference, this procedure had the significant disadvantage of being limited to drugs of relatively small doses.
U.S. Pat. No. 4,871,549, also incorporated herein by reference, discloses one method of preparing a sustained release composition. Pellets incorporating a swelling agent are coated with an outer membrane. The swelling agent absorbs fluid and the outer membrane breaks, releasing the drug quickly from each pellet.
A need exists for new and improved methods and compositions which administer drugs in a sustained fashion. Particularly with respect to proteins such as somatotropins, which are most effective when administered over a period of days or weeks, there is a need for such processes and compositions.